Calcium and sodium recovery from microwave‐pretreated red mud with added solid ammonium chloride

Abstract

AbstractBACKGROUNDMany studies have used an NH4Cl solution as a solvent during microwave‐assisted metal leaching processes. However, in this study, solid NH4Cl instead of an NH4Cl solution was used as a chlorinating agent during the microwave pretreatment of red mud to induce a rapid temperature increase by minimizing heat loss by water. Red mud only and red mud–solid NH4Cl samples were pretreated by microwaves under various conditions. Leaching tests were then conducted on the microwave‐pretreated red mud only and red mud–solid NH4Cl samples using deionized (DI) water as a leaching solution.RESULTSThe leached Ca and Na concentrations from the microwave‐pretreated red mud–solid NH4Cl samples were significantly higher than those from the microwave‐pretreated red mud only samples at the given test conditions. In contrast to the red mud only samples, the leached Ca and Na concentrations from the microwave‐pretreated red mud–solid NH4Cl samples increased with increasing microwave output power. The leached Ca and Na concentrations from the microwave‐pretreated red mud–solid NH4Cl samples at 5000 W were significantly higher than those from the microwave‐pretreated red mud–solid NH4Cl samples at 500 and 1100 W and from the non‐microwave‐pretreated red mud–solid NH4Cl samples.CONCLUSIONAdding solid NH4Cl to the red mud during the microwave pretreatment process is effective to recover Ca and Na at a microwave output power of 5000 W. The leached solutions with elevated Ca and Na concentrations from the microwave‐pretreated red mud–solid NH4Cl samples at 5000 W can be used for aqueous mineral carbonation to sequester CO2. © 2019 Society of Chemical Industry